The present invention generally relates to alternators of the type that are used in vehicles to provide electrical power for running accessories and charging batteries. More particularly, this invention relates to an improved permanent magnet rotor portion for use by the alternators and other electric machines.
Typical rotor configurations that are used in alternators are disclosed in U.S. Pat. Nos. 5,693,995, 5,710,471, 5,747,909 and 5,753,989.
In one aspect, the present invention is directed to a rotor for an electric machine comprising a plurality of independent poles and permanent magnets circumferentially arranged in an alternating configuration such that each permanent magnet is positioned intermediate a pair of consecutive or successive independent poles. The arrangement of the permanent magnets and independent poles defines an outer rotor perimeter and a central opening for receiving a shaft upon which the rotor rotates. Each independent pole has a generally triangular cross-section that defines an apex portion that confronts the central opening and an end portion that forms a portion of the outer rotor perimeter. Each permanent magnet has a first end for confronting the central opening, and a second end that forms a portion of the outer rotor perimeter. Each permanent magnet tapers from the first end to the second end. This particular geometry of each permanent magnet is referred to herein as xe2x80x9creverse trapezoidalxe2x80x9d. An important feature of the rotor of the present invention is that the centrifugal force produced by rotation of the rotor radially pushes each permanent magnet away from the central opening. Furthermore, the aforementioned centrifugal force cooperates with the shape of the independent poles and permanent magnets to further improve the integrity of the lodgment of each permanent between the corresponding pair of consecutive independent poles. Each pair of consecutive independent poles are separated by a space that has a shape that conforms to the shape of a corresponding permanent magnet that is positioned within the space.
The rotor of the present invention further comprises a pair of hubs. The permanent magnets and independent poles are positioned between the hubs. The independent poles are at to the hubs in such a manner that there is no interconnection between the apex portions of the independent poles so as to induce magnetization having a direction that is substantially orthogonal to the radius of the rotor.
The permanent magnets are formed from a magnetic material chosen from ferrite, neodymium, ceramic and samarium-cobalt
In a related aspect, the present invention is directed to rotor for an electric machine, comprising at least two independent poles and at least two permanent magnets arranged in an alternating configuration such that each permanent magnet is positioned intermediate a pair of consecutive or successive independent poles. The arrangement of the permanent magnets and independent poles defines an outer rotor perimeter and a central opening for receiving a shaft upon which the rotor rotates. Each independent pole has a fit end portion that confronts the central opening and a second end portion that forms a portion of the outer rotor perimeter. The second end portion of each independent pole has a pair of lips that conform to the locally defined curvature of the outer rotor perimeter. Each permanent magnet has a first end for confronting the central opening and a second end that forms a portion of the outer rotor perimeter. Each lip of the second end portion of each independent pole abuts a portion of the second end of a corresponding permanent magnet, whereby the centrifugal force produced by rotation of the rotor radially pushes each permanent magnet away from the central opening and whereby the centrifugal force cooperates with the independent poles and permanent magnets to further improve the integrity of the lodgment of each permanent magnet between the responding pair of independent poles. Each pair of consecutive or successive independent poles are separated by a space that has a shape that conforms to the shape of a corresponding permanent magnet that is positioned within the space. In one embodiment, each permanent magnet has a reverse trapezoidal cross-section. In another embodiment each permanent magnet has a generally cross-section.